Conventionally, for a halved sliding bearing, two of which are paired into a cylindrical shape and which has a bearing alloy layer, serving as a sliding surface, on the inside of a steel back metal, a flash plating layer (also referred to as “coat layer”) has been deposited so as to coat the outer back surface of the steel back metal opposing to the inner peripheral surface on which the bearing alloy layer is formed and side edges thereof or the whole surface of steel back metal, as described e.g. in JP-A-6-74238 (see claim 6, paragraph [0006]) and JP-A-2002-513890 (see paragraph [0016]). The flash plating layer is deposited to prevent the steel back metal from corrosion and to give the steel back metal a bright and attractive appearance. As the flash plating layer, a plating layer of Sn, Pb or an alloy thereof having a thickness of 0.1 to 10 μm is used.
The above-described halved sliding bearing 1′ is fitted on the inner surface of a bearing housing, for example, comprising a connecting rod 2 connected to a crankshaft of an internal combustion engine and a connecting rod cap 3, as shown in FIG. 2. The bearing housing comprising a connecting rod 2 and of the connecting rod cap 3 is subjected to repeated stress of compression and tension by dynamic load during the internal combustion engine operation. In particular, rigidity of the connecting rod has been lowered since the weight of internal combustion engine is reduced in recent years. In the case where the elastic deformation of the bearing housing increases with the decrease in rigidity, a relative slide occurs between the back surface of the halved sliding bearing 1′ and the inner surface of the bearing housing. Furthermore, heat is generated on the inner surface of the halved sliding bearing 1′ due to friction caused by sliding with a shaft. If the conventional coat layer of Sn, Pb or an alloy thereof melts accordingly, the coat layer flows under a bearing back surface pressure (radial stress) caused by an interference for fixing the halved sliding bearing 1′ to the bearing housing or stress caused by sliding, and it aggregates locally at a low-pressure portion as deformedly shown in FIGS. 3A and 3B. Since the volume of Sn, Pb or the alloy thereof increases when melt, so that the flow amount thereof increases. Therefore, the volume of an aggregating part increases locally, which swells the sliding surface of the halved sliding bearing 1′ to the inner surface side. Therefore, there arises a problem that the halved sliding bearing is liable to come into strong contact with the shaft.